Method and mobile marine platform apparatus having floating submerged mat stabilization

ABSTRACT

Three levels in a vertical plane, being an elevated work platform, a middle hull and a submersible lower hull are connected together by six telescoping vertical support columns. The lower catamaran hull consists of two pontoon-type tubes connected together by a mat having freeing holes therein to reduce the mat&#39;&#39;s resistance in the vertical plane when submerged. The middle hull is maintained above the water level when the lower hull is at the surface of the water, but settles down into the water to provide buoyant support when the lower hull is submerged. The lower hull, being buoyant and ballastable, is raised or lowered in the water by adding or removing water ballast. Action snubbers are provided to work in conjunction with the vertical columns to prevent any quick or fast relative movement between the lower hull and the combined middle hull and upper deck structure. An alternative embodiment utilizes the middle buoyant hull to floatably support a three column structure. Other alternative embodiments include non-telescoping columns, single column platform apparatus and means for varying the amount or number of freeing holes used to affect the mat resistance in the water.

United States atent Harper [54] METHOD AND MOBILE MARINE PLATFORMAPPARATUS HAVING FLOATING SUBMERGED MAT STABILIZATION [72] Inventor:James C. Harper, Houston, Tex.

[73] Assignee: Dresser Industries, Inc., Dallas, Tex.

[22] Filed: March 17, 1970 211 App]. No.: 20,278

Related US. Application Data [63] Continuation-in-part of Ser. No.872,314, Oct. 29,

1969, abandoned [52] US. Cl. ..114/0.5 D, 114/435 [51] Int. Cl. ..B63b35/00, B63b 35/44 [58] Field of Search ..114/0.5 D,43.5,77, 125,124,114/665 R, 0.5 R; 61/465 [56] References Cited UNITED STATES PATENTS3,442,239 5/1969 Wilson ..l l4/0.5 D 3,207,110 9/1965 Laborde et al....1 l4/0.5 D 3,515,084 6/1970 Holmes ..1l4/0.5 D

Primary Examiner-Trygve M. Blix Attorney-Robert W. Mayer, Thomas P.Hubbard, Jr., Daniel Rubin, Raymond T. Majesko, Roy L. Van Winkle,William E. Johnson, Jr. and Eddie E. Scott [57] ABSTRACT Three levels ina vertical plane, being an elevated work platform, a middle hull and asubmersible lower hull are connected together by six telescopingvertical support columns. The lower catamaran hull consists of twopontoon-type tubes connected together by a mat having freeing holestherein to reduce the mats resistance in the vertical plane whensubmerged. The middle hull is maintained above the water level when thelower hull is at the surface of the water, but settles down into thewater to provide buoyant support when the lower hull is submerged. Thelower hull, being buoyant and ballastable, is raised or lowered in thewater by adding or removing water ballast. Action snubbers are providedto work in conjunction with the vertical columns to prevent any quick orfast relative movement between the lower hull and the combined middlehull and upper deck structure. An alternative embodiment utilizes themiddle buoyant hull to floatably support a three column structure. Otheralternative embodiments include non-telescoping columns, single columnplatform apparatus and means for varying the amount or number of freeingholes used to affect the mat resistance in the water.

20 Claims, 18 Drawing Figures P'A'TENTEDJUL] I972 SHEET 1 [F9 "Him;

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' sum ans 9 RACHET I42 CONTROL UP DOWN RACHE-T RACHET l25 I FlawsINVENTOR JAMES C. HARPER ATTORNEY METHOD AND MOBILE MARINE PLATFORMAPPARATUS HAVING FLOATING SUBMERGED MAT STABILIZATION RELATEDAPPLICATION This application is a continuation, at least in part, of myUS. application Ser. No. 872,314, filed Oct. 29, 1969 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates, generally, to mobilemarine platform apparatus, and specifically, to a structure havingimproved stability, whether in the transit or in the working positions,and which is easily transportable to an offshore location, as well as toa method of maintaining stability of a mobile marine platform apparatus.

The offshore petroleum exploration art has long recognized the need forimproved stability in mobile marine platforms such as might be used indrilling, workover, salvage operations and the like. Despite manyattempts by those in the art to fill this need, the prior art structureshave failed to achieve stability in both the transit and the workingpositions. Thus, in achieving stability for working, stability intransit was sacrificed, and vice versa. Further, even the optimizedstability of such structures failed to provide adequate stabilization inheavy seas.

It is therefore the primary object of the present invention to provide anew mobile marine platform apparatus having improved stability, both inthe transit and in the working positrons.

It is another object of the invention to provide an offshore platformapparatus having new and improved apparatus for converting from thetransit to the working position and vice versa.

It is yet another object of the invention to provide a new apparatusproviding stability for marine platforms, such apparatus beingmaintained off the ocean floor in the working position of the platform.

It is still another object of the invention to provide a mobile marineplatform apparatus having flexible submerged means which in combinationwith other unique apparatus described herein have time constants longerthan that of the longest ocean waves to provide increased stability ofthe platform apparatus.

It is another object of the invention to provide a new and improvedmethod for improving the stability of floating, mobile marine platformapparatus.

The objects of the invention are accomplished, briefly, by a mobilemarine platform apparatus having a buoyant, ballastable structureassociated with a telescoping columnar support structure such that theoverall height of the apparatus is not severely increased for thetransit phase of the operation. A second buoyant structure, maintainedabove water level during the transit mode, provides buoyant support whenthe lower structure is submerged. A mat structure maintained off theocean floor, and a new and improved method for using same, providesincreased stability for the working phase of the operation. Actionsnubbing members between the pontoon structure and the upper deck addeven further stability to the offshore platform apparatus. Throughoutthe various embodiments, a floating, submerged mat structure providesvastly increased stabilization.

These and further objects, features and advantages of the presentinvention will be apparent from a reading of the following detaileddescription and accompanying drawing, in which:

FIG. 1 is a side elevational view of a complete embodiment of theapparatus according to the invention while in the transient mode ofoperation;

FIG. 2 is a similar view showing the apparatus in the working mode ofoperation with its pontoon structure lowered;

FIG. 3 is a bow elevational view of the apparatus according to FIG. 2;

FIG. 4 is a plan view of the mat and pontoon structure according to theinvention as illustrated in FIGS. 1-3;

FIG. 5 is a side elevational view of an alternative embodiment of theapparatus according to the invention while in the transit mode ofoperation;

FIG. 6 is a side elevational view of an additional alternativeembodiment of the apparatus according to the invention in the workingmode of operation;

FIG. 7 is a plan view of the mat and pontoon structure according to theinvention as illustrated in FIG. 6;

FIG. 8 is a plan view of an alternative mat and pontoon structureaccording to the invention as illustrated in FIG. 6;

FIG. 9 is an elevational view of the action snubber associated with oneor more of the support columns according to the invention;

FIG. 10 is a more detailed cross-sectional view of a portion of theaction snubber illustrated in FIG. 9;

FIG. 11 is a detailed cross-sectional view of a portion of analternative action snubber;

FIG. 12 is a side elevational view of an alternative embodiment of theapparatus according to the invention;

FIG. 13 is a plan view of the mat structure according to the apparatusof FIG. 12;

FIG. 14 is a side elevational view of an alternative embodiment oftheapparatus according to the invention;

FIG. 15 is a plan view of the mat structure according to the apparatusof FIG. 14;

FIG. 16 is a side elevational view of an alternative embodiment of theapparatus according to the invention while in the transit mode;

FIG. 17 is a similar view of the apparatus of FIG. 16 but having itslower structure further submerged in the water; and

FIG. 18 is a schematic view, partly in section, of apparatus accordingto the invention useful in lowering, raising, and maintaining stabilityof the columns.

Referring now to the drawing in more detail, especially to FIG. 1, thereis illustrated a side elevational view of the apparatus 10 illustratedin the transit mode of operation. The apparatus 10 includes an elevatedwork platform I2 which is positioned above the surface 14 of the oceanat all times in normal use. As will be explained hereinafter, theplatform 12 can be maintained fairly flat, with a low profile, exceptfor the superstructure area 16 associated with the crew s quarters andauxiliary equipment such as the illustrated crane assembly. Although notillustrated, a drilling derrick, mast, or other rig equipment can alsobe mounted on the platform 12, for example, as in U. S. Pat. No.3,078,680 to Wepsala issued on Feb. 26, 1963.

The platform 12 is supportedly mounted on six vertical telescopingcolumns 18 which in turn are connected to two buoyant, ballastablestructures 20, three columns to each structure 20 (better seen in FIG.4). Each of the pontoon structures 20 is equipped with a propeller 22for causing the apparatus I0 to move through the seas in the transitmode. The propellers 22 can be driven by a conventional power plant andtransmission (not shown) from the superstructure area 16. It should beappreciated that a guidable rudder (not shown) can be suitably disposedon the structure 20 if desired to aid the propellers 22 in guiding theapparatus 10 while underway. It should further be appreciated that theapparatus 10 can also be placed on location by other conventional means,such as with the employment of tugs and/or other assisting equipment ifit be desired to aid or even eliminate the internal propulsion system.

Attached intermediate the upper and lower ends of the columnar members18 is a buoyant structure 24, comprising, for example, one or morecounter-buoyancy tanks. As shown in FIG. I, the buoyant structure 24 isabove the water level 14 during the transit mode of operation. Thisstructure 24 runs both fore and aft, on both sides of the apparatus, andalso transverse, as viewed in FIG. 3.

FIG. 2 illustrates the apparatus 10 in the working mode of operation,i.e., with the pontoon structure 20 ballasted down beneath the surface14 of the water. Means for selectively and controllably ballasting anddeballasting the structure 20 are well known in the art and need not bementioned here in detail except to note that the inner tube 26 of column18 telescopes within the outer tube 28 of column 18, the telescopingaction being solely a function of ballasting or deballasting thestructure 20, as by adding or pumping out seawater. It should beappreciated, however, that the upper end of column 18 is fix edlysecured to the upper platform structure 12, whereas the lower end ofcolumn 18 is fixedly secured to the ballastable structure 20. As ballastis added'to the structure 20, it begins to be submerged beneath thesurface of the water. The initial partial flooding of the structure 20causes the apparatus to take a new waterline near the buoyant structure24 and continued flooding extends the columns 18 further beneath thewater. When fully extended, the columns come against heavy stops (notshown) which align the upper and lower units of the apparatus, andprevents further extension. Continued flooding, after the column stopshave been reached, brings the apparatus 10 to the desired workingwaterline.

It should be appreciated that the ballast pumps (not shown) bring aboutthe apparatus change in configuration. Removal of the ballast returnsthe structure to the waters surface since no column lock is necessary inthe fully extended position, i.e., the weight of the ballast watermaintains the columns fully extended. However, as explained hereinafterwith respect to FIG. 18, it is sometimes helpful to use rachet means, orthe like, while raising, lowering, or maintaining the lower struc turesubmerged.

FIG. 3 illustrates a bow elevational view of the apparatus 10 in theworking position, i.e., with ballast added to the ballastable structure20. As will be better seen in FIG. 4, a mat structure 30, with supportframes 32, extends between the pontoons 20. As will be explainedhereinafter with respect to FIGS 9, I0, and 11, the action snubbers 60help provide additional stability to the apparatus 10 in heavy seas. Itshould be appreciated that a blow elevational view (now shown) of theapparatus 10 in the transit mode would show a catamaran configuration,wherein the mat 30 and buoyant structure 24 are preferably completelyout of the water to provide improved towing characteristics.

FIG. 4 illustrates in a plan view the mat 30 connecting the two pontoonstructures 20. The mat 30 is actually comprised of a pair of mats havinga plurality of freeing holes 31 therein to lessen the resistance of themat to vertical movement in the water. However, if desired the mat 30could be one continuous (except for the holes 31) member, without thegap 33 as illustrated. The cross frames 32 are used to provideadditional strength for the overall structure. Furthermore, asillustrated and described hereinafter, the mat 30 can be a solidstructure (no holes 31) if desired.

FIG. 5 illustrates an alternative embodiment of the apparatus accordingto the invention, wherein the tip ends of the columns 18 are notnecessarily fixedly secured to the platform structure 12. Thus, itshould be appreciated that the platform 12 can be supportedly mounted tothe buoyant structure 24 solely by the support members 34 if desired.

FIG. 6 illustrates an alternative embodiment of the apparatus accordingto the invention, wherein an apparatus 40, having a working platform 41,is affixed to the top ends of three columnar buoyant support members 42,which may be telescoping if desired. Fixedly secured to the bottom endsof each of the columns 42 is a circular, doughnut-shaped" pontoonstructure 43, shown in a plan view in FIG. 7, and partially incross-section in FIG. 6. As with the other ballastable structuresdescribed herein, the structure 43 can be ballasted and deballasted tocontrol its level within the water.

Fixedly secured intermediate the bottom and top ends of the buoyantcolumns 42 is a buoyant structure 44 providing buoyancy for theapparatus 40 since it is shown in the fully extended, working position.Thus, with the buoyant structure 43 in the fully extended position, thestructure 44 and columns 42 buoyantly support the apparatus 40, theentire vessel with its submerged extension being maintained above theocean floor 45.

To move the apparatus 40 to the transit mode of operation, water ballastis pumped from the structure 43 to either bring it to the surface or atleast closer to the surface of the water. In either event, this actioncauses the intermediate floatation structure 44 to be raised out of thewater to facilitate moving the apparatus 40, either by its own power orotherwise.

FIG. 7 illustrates a top plan view of the ballastable structure 43. Amat 50, having a plurality of freeing holes SI, or, alternatively havingno freeing holes, relieves some of the resistance to vertical movementsin the water. The cross frame members 52 provide additional structuralstrength to the overall apparatus.

FIG. 8 illustrates an alternative embodiment for the pontoon structureuseful with the apparatus according to FIG. 6. Individual ballastablepontoon members 53 are provided for each of the columns 42, instead ofhaving a single continuous ballastable structure as illustrated in FIG.7. A mat 54, having a plurality of freeing holes 55, provides additionalstability to the overall apparatus in manner analogous to the otherembodiments described herein. The cross beams 56 and circumferentialbeam 57 provide additional strength to the overall apparatus.

FIG. 9 illustrates in an elevational view an action snubber 60positioned relative to the columnar support member 18. In general, theaction snubber 60 is comprised of cylinder 61 attached at its lower endto the pontoon 20. An internal piston 62 has a piston rod 63 attached atits upper ends to the sleeve 28 of the column 18. It should beappreciated, however, that the piston rod 63 could be alternativelyattached to the pontoon 20 and the cylinder 61 to the sleeve 28. Thefully extended length of the cylinder and piston rod is chosen to begreater than the predetermined distance that the column 18 can beextended to prevent a tension load being applied to the action snubber.

The action snubber 60 is filled with a fluid, for example, hydraulicoil, water or another suitable fluid 64. Means are provided, as isexemplary illustrated in FIGS. 10 and 11, to allow the fluid 64 to bedisplaced from the piston rod end to the blind end, or vice versa, and atank 65 is provided, with suitable valving, to add fluid to the cylinderor to allow fluid to be displaced from the cylinder 61.

While the preferred embodiment of the invention contemplates the use ofone or more such action snubbers with each of the columns 18, a fewernumber can be used ifdesired. The four comer columns 18, in the case ofthe apparatus described in FIGS. 1 and S are the most important inproviding optimized stability. It should be appreciated that thesnubbers can be placed inside the columns 18 or mounted external to themin a multiplicity of effective locations. The action snubbers can beattached to the lower hull 20, as well to the upper sleeve 28 of thecolumn 18, by welding, with pins, bolts or any such manner.

In the operation of the snubbers, it should be appreciated that theyprevent any quick or fast relative movement between the lower pontoonstructure 20 and the middle buoyant structure 24. In the working mode ofoperation, the mat 30 and pontoon structure 20 are below the surface ofthe water and are not subject to weather reactions such as are caused bywind and wave. As the intermediate structure 24 and upper deck 12attempt to rise or fall with a swell or wave, the submerged mat 30 andpontoon structure tend to remain stable at a depth where the amplitudeof the wave action is considerably reduced.

However, without the action snubber or some analogous means, the columnsI8 would be constantly extending and retracting. In so doing, the upperstructures would move about with instability despite the stability ofthe submerged structure. That is, the stability of the submergedstructure would not be transferred to the upper structures. With theaction snubbers, the submerged and surface structures react as onestructure, improving the vertical steadiness of the entire vessel.

The movement of fluid within the snubber is controlled by the size ofthe component parts thereof. The preferred embodiment contemplates thesnubber action requiring about two minutes (120 seconds) end-to-end, ascompared to the longest seas, such as in swells having periods ofapproximately seconds. With such an arrangement, the stability of themat 30, with its plurality of freeing holes, is transferred to the upperstructures 24 and 12. Since the overall apparatus is designed to have anextremely long natural period, as compared to the longest waves, theresult is a small vertical movement, if at all, even in long swells andrough seas.

It should be appreciated, however, that the action snubber does notassist in lowering or raising the pontoon structure and mat 30. It doesmaintain the relationship between the submerged and upper structuresafter the columns 18 are extended, since the ballast is a pre-tensionload. Also, the snubbers control the rate of sinking and of re-floatingthe pontoons 20.

Referring again to FIG. 2, a plurality of cup-shaped compartments 70 areformed in the pontoon structure 20, one for each of the columns 18. Thelower end 71 of the upper sleeve 28 is rounded to fit within thecompartment 70. The column 18 is also formed to correspond to the shapeof the pontoon 20, as is seen in FIG. 3.

The effect of the columns 18 extending during ballasting is the same asif upper structures 12 and 24 were relieved of the weight of pontoon 20,and the upper structures may become quite active during the ballastingoperation due to surface wind and waves. The rise and fall of the upperstructures may extend and retract the columns 18 at this point in thecycle. Should this happen, the cushion chamber 70 prevents the two partsfrom slamming together with any real damaging force. As the shaped endportion 71 enters the cushion chamber 70, it must clear out the watertrapped therein. The clearance between the two parts is sized to permitthe column ends 71 to enter the compartment 70 relatively slowly andthus prevent damage.

Referring now to FIG. 10, there is illustrated a portion, in crosssection of an exemplary action snubber 60. This piston 62, mounted onthe piston rod 63, has an orifice 80 in the end thereof and a pair ofholes 81 and 82 in the sides of the hollow portion -83 of the piston rod63. Thus, as explained with respect to FIG. 9, the movement of thepiston 62 is slowed down an appreciable amount as the fluid passesthrough the orifice 80 and holes 81 and 82, the direction of fluid flowbeing dependent upon relative movement between the submerged pontoonstructure 20 and the upper structures 24 and 12.

FIG. 11 illustrates an alternative piston configuration for an actionsnubber according to the invention, the piston 85 having an orifice 85dividing into two passageways 87 and 88 for allowing fluid exchange asthe piston is moved in either direction.

Although not illustrated, other action snubbers for use with apparatusaccording to the invention will become apparent from the embodimentsillustrated. For example, instead of flowing through the piston, thepiston can be sized to permit fluid to flow around it to either end ofthe cylinder. Also, an external piping arrangement connecting the twoends of the cylinder produces analogous results.

FIG. 12 illustrates a side elevational view of an alternative apparatus90 illustrated in the working mode of operation. The apparatus 90includes an elevated work platform 91 which is positioned above thesurface 14 of the ocean at all times in normal use. The platform 91 issupportedly mounted on a plurality of buoyant columns 92, for examplesix columns, which in turn are connected to a lower mat structure 93(shown in plan view in FIG. 13). The mat 93 can be ballastable anddeballastable, as with the pontoon structures 20 in FIG. I, but has alarge surface area to maintain stability in a vertical direction.Alternatively, the mat 93 can be a large area plate, with or withoutfreeing holes, supportedly attached to one or more pontoons which areballastable and deballastable. Alternatively, the columns 92 can beballasted and deballasted to cause the mat 93 to be moved vertically inthe water without the use of a ballastable mat or ballastable pontoons.

FIG. 13 illustrates in plan view the mat structure 93 supportedlyattached to the columns 92, shown in cross section. In the preferredembodiment of the mat 93, the mat is ballastable and deballastable, asby adding or removing air (or water) from the mat. A center hole 94 islocated in the center of the mat 93 for access to the ocean bottom, forexample, to provide a means for drilling an oil or gas well. Quiteobviously, the hole 94 can be beneath a similar hole (not illustrated)in the work platform 91 of FIG. 12. Alternatively, the mat 93 could bewithout the hole 94 and have the drilling or workover operationsperformed over the sides of the vessel.

In the operation of the apparatus of FIGS. [2 and I3, ballast is addedto the mat 93 (or to the supporting pontoons, not shown) or to thecolumns 92, whereupon the columns 92 begins sinking further into thewater. Ballast is added until the mat 93 is an adequate depth beneaththe surface of the water, but always maintained floating; that is, offthe ocean floor. For purposes of this specification, floating" isintended to mean that a structure is maintained off the ocean floor, butnot necessarily on the ocean surface. It should also be appreciated hatthe mat structures in the different embodiments herein are preferablymaintained horizontal, and thus are parallel to the elevated workplatforms and to the surface of the water.

It should be appreciated that the mat 93 provides a vastly improvedstabilization characteristic because of the huge volume of water betweenthe mat and the ocean surface. For example, if the mat is 100 ft. wide,and 200 ft. long, submerged in 100 ft. of water, there are two millioncubic feet of water resting on the mat, all of which has to be displacedto move the vessel in the vertical direction, up or down. Hence. whenthe apparatus is used in heavy seas, the apparatus remains nonethelessquite stable.

It should likewise be appreciated that the absence or presence of thefreeing holes in the mat is a factor in the stability characteristics ofthe apparatus, since the surface area of the mat is directly affected bysuch holes, and also by the access hole 94 shown in FIG. 13.

FIG. 14 illustrates a side elevational view of an alternative apparatus95 illustrated in the working mode of operation. The apparatus 95includes an elevated work platform 96 which is positioned above thesurface 14 of the ocean at all times in normal use. The platform 96 issupportedly mounted on a single column 97, which may or may not beballastable, which in turn is connected to a lower mat structure 98(shown in plan view in FIG. 15). The mat 98, as with the previouslydiscussed mat structures, can be ballastable and deballastable.Alternatively, the ballast feature can come from a pair of pontoons 99,or perhaps a single circumferential pontoon as illustrated in FIG. 7.Alternatively, the ballast feature can come from ballasting anddeballasting the single column 97. In any event, the large surface areaof the mat 98, with or without the freeing holes 100, causes theapparatus 95 to have vastly improved stabilization, especially in viewof a single column being exposed to the action of the waves. Fordrilling access, a hole 101 can be provided in the mat 98 to coincidewith a similar hole 103 in the work platform 96.

In FIG. 15, the mat 98 is illustrated as having a number of freeingholes 100, but having some of the holes closed, as with a metal plate102. The plate could be welded, hinged and locked, or any other suchmeans as to close the hole. Alternatively (not illustrated), the holesalso could be selectively closed with a shutter mechanism. In any event,depending upon the wave action and time period, it may be desirable toselectively open or close a given number or geometry pattern of thefreeing holes to provide optimum stabilization, even to the point ofclosing all the holes and effectively having a solid mat. It should beappreciated that the column 97 can be telescoping if desired, in themanner of the telescoping columns in FIG. 1. Likewise, an intermediatefloatation structure could be added to the columns 97 if desired, in themanner of structure 24 in FIG. I.

In the operation of the apparatus of FIGS. 14 and 15, ballast is addeduntil the column 97 and mat structure 98 is an adequate depth beneaththe surface of the water but always maintained floating. To return tothe transit mode of operation, the ballast is removed, causing the matto be raised vertically in the water to some desired level.Alternatively, the apparatus could be towed with the mat submerged tothe working depth.

FIG. 16 illustrates a side elevational view of an alternative apparatus110 in the transit mode of operation. The apparatus 110 includes anelevated work platform 111 which is positioned above the surface 14ofthe ocean at all times in normal use. As compared with the apparatusof FIG. 1, in which the platform profile remains fairly constant, theprofile of the apparatus 110 is seen to change as the columns 112 extendthrough the platform 111. Except during the times the columns 112 aremoving with respect to the platform 111, the columns are locked into theplatform 111, for example, with lock pins (not shown). An intermediatebuoyant member 113 is fixedly attached to the platform 111 by means ofthe support structures 114. Attached to the lower end of the columns 112is a mat structure 115, the mat 115 being ballastable and deballastableto cause the mat to sink further into the water. Alternatively, the mat115 can be a non-ballastable plate supportedly attached to a ballastableand deballastable pontoon structure (not shown). Alternatively, thecolumns 112 can be ballastable and deballastable to cause the mat 115 torise or sink further into the water.

FIG. 17 illustrates a side elevation view of the apparatus 110 in theworking mode of operation.

In the operation of the apparatus 110, ballast is added until theintermediate member 113 settles down into the water. After the lock pinsare removed, additional ballast causes the mat 115 to continue sinkingin the water. At the desired depth, the operations of the vessel, forexample drilling, may be commenced. As with the other mat structuresdescribed herein, the submerged, floating mat provides vastly improvedstabilization in heavy seas. When it is desired to reverse theoperation, ballast is removed and the column 112 begins to move upthrough the platform 111. At a given point, the lock pins arereinserted. Additional loss of ballast then causes the intermediatestructure 113 to be lifted out of the water to facilitate towing in thetransit mode of operation.

FIG. 18 illustrates schematically a means for aiding the raising,lowering and maintaining of the mat structures variously describedherein. The column 120 has a series of rachet teeth 121 on one side ofthe column and a second series of rachet teeth 122 on the other side ofthe column. For ease of illustration, the column 120 is shown as beingmovable with respect to an elevated work platform 123, such as would bethe case in an apparatus as is illustrated in FIGS. 16 and 17. However,those skilled in the art will appreciate the double racheting means asbeing readily adaptable to the telescoping columnar configuration ofFIG. 2, wherein one portion of the telescoping column can be controlledwith respect to the other portion.

Referring again to FIG. 18, the column 120 is seen to pass through ahole 124 in the platform 123. Fixedly attached to the platform 123 is apair of air cylinders 125 and 126. The DOWN RACI-IET" cylinder 125 has apiston rod 127, to which a rachet dog 128 is pivotally attached by pin129. A spring 130 is attached to both the piston rod 127 and the rachetdog 128. In operation, the dog 128 can pivot down against the spring130, but is blocked from pivoting up against the piston rod 127.

In a similar manner, the UP RACHET" cylinder 126 has a piston rod 135,to which a rachet dog 136 is pivotally attached by pin 137. A sPring 138is attached to both the piston rod 135 and the rachet dog 136. Inoperation, the dog 136 can pivot up against the spring 138, but isblocked from pivoting down against the piston rod 135.

The air cylinders 125 and 126 are each connected by compressed airlines140 and 141 to a rachet control panel 142.

In the operation of the racheting apparatus of FIG. 18, if the aircylinders and 126 are both activated, the pistons 127 and are extended,the dogs 128 and 136 are engaged, respectively, with the rachet teeth121 and 122, and the column 120 will not move with respect to theplatform 123. If it is desired, to move the column 120 down, the aircylinder 126 is deactivated, thus disengaging the rachet dog 136. Theballast being added to the lower section of the column, the mat forexample (not shown in FIG. 18), thus causes the column 120 to move downwith respect to the platform 123. However, since the column cannot moveup because of the engaged rachet assembly, the system will not respondup and down to the heavy seas. The column can only go down. In ananalogous manner, in raising the column, the air cylinder 126 is theonly one activated, thus allowing the column to move up only. Should themat be in the desired position, such as fully extended down, bothcylinders can be activated to prevent movement in either direction. Itshould be appreciated that the double racheting mechanism can be used,if desired, in conjunction with the action snubber systems elsewheredescribed herein.

Thus there has been illustrated and described herein varioussemi-submersible offshore vessels having vastly improved stabilitycharacteristics during the working mode of operation, some of which havethe catamarans stability and speed on the surface during the transitmode. By having a submerged mat structure maintained off the oceanfloor, the entire apparatus is observed to be only slightly affected bythe most severe weather. Again, by using action snubbers in cooperationwith the telescoping columns designed to have time constants longer thanthe longest seas, an even higher degree of stability is achieved.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A mobile marine platfonn apparatus, comprising:

a platform structure adapted to support supplies and equipment;

a plurality of telescoping columnar members, each being fixedly securedat its upper end to said platform structure;

a buoyant, ballastable structure fixedly secured to the lower end ofeach of said columnar members, including means to ballast and deballastsaid ballastable structure to submerged and floating positions,respectively; and

a second buoyant structure fixed intermediate the ends of at least oneof said columnar members to floatably support said platform apparatuswhen said ballastable structure is submerged a predetermined distance.

2. A mobile marine platform apparatus, comprising:

a platform structure adapted to support supplies and equipment;

a plurality of telescoping columnar members, each being fixedly securedat its upper end to said platform structure;

a buoyant, ballastable structure fixedly secured to the lower end of atleast one of said columnar members, including means to ballast anddeballast said ballastable structure to submerged and floatingpositions, respectively, and

a second buoyant structure fixed intermediate the ends of at least oneof said columnar members to floatably support said platform apparatuswhen said ballastable structure is submerged a predetermined distance.

3. A mobile marine platform apparatus, comprising:

a platform structure adapted to support supplies and equipment;

a plurality of telescoping columnar members, each being fixedly securedat its upper end to said platform structure;

a plurality of buoyant, ballastable structures, each of said ballastablestructures being fixedly secured to the lower end of at least one ofsaid columnar members, including means to ballast and deballast saidballastable structures to submerged and floating positions,respectively; and

a flotation structure fixed intermediate the ends of at least one ofsaid columnar members to floatably support said platform apparatus whensaid ballastable structures are submerged a predetermined distance.

4. The apparatus according to claim 3 wherein said plurality ofballastable structures comprises a pair of parallel pontoons.

5. The apparatus according to claim 4, including in addition thereto, aperforated mat connected between said parallel pontoons.

6.A mobile marine platform apparatus, comprising:

a platform structure adapted to support supplies and equipment;

a plurality of telescoping columnar members;

a buoyant, ballastable structure fixedly secured to the lower end of atleast one of said columnar members, including means to ballast anddeballast said ballastable structure to submerged and floatingpositions, respectively; and

a second buoyant structure fixed intermediate the ends of at least oneof said columnar members to floatably support said platform apparatuswhen said ballastable structure is submerged a predetermined distance,said platform structure being fixedly attached to said second buoyantstructure.

7. A mobile marine platform apparatus, comprising:

a platform structure adapted to support supplies and equipment;

a plurality of columnar members;

a buoyant, ballastable structure comprising a plurality of pontoons, andincluding in addition thereto, a perforated mat connected between saidpontoons, fixedly secured to the lower end of at least one of saidcolumnar members, including means to ballast and deballast saidballastable structure between varying depths of submersion;

a second buoyant structure fixed intermediate the ends of at least oneof said columnar members to floatably support said platform apparatuswhen said ballastable structure is submerged a predetermined distance,said platform structure being fixedly attached to said second buoyantstructure.

8. A mobile marine platform apparatus, comprising:

a platform structure adapted to support supplies and equipment;

a plurality of columnar members;

a buoyant, ballastable structure comprising a pontoon having a centerportion comprised of a perforated mat, fixedly secured to the lower endof at least one of said columnar members, including means to ballast anddeballast said ballastable structure between varying depths ofsubmersion;

a second buoyant structure fixed intermediate the ends of at least oneof said columnar members to floatably support said platform apparatuswhen said ballastable structure is submerged a predetermined distance,said platform structure being fixedly attached to said second buoyantstructure.

9. A mobile marine platform apparatus, comprising:

a platform structure adapted to support supplies and equipment;

a plurality of telescoping columnar support members, each being fixedlysecured at its upper end to said platform structure, whereby the profileof the platform remains substantially constant regardless of thetelescoping positions of said support members; and

submersible means fixedly secured to the lower ends of said supportmembers for extending said support members beneath the sea whilemaintaining said platform structure at or above the surface of the sea.

10. The platform apparatus according to claim 9, including in additionthereto at least one action snubber member connected between saidplatform structure and said submersible means.

11. The platform apparatus according to claim 10 wherein said actionsnubber comprises a liquid filled piston and cylinder having means forsaid fluid to move from one end of said cylinder to the other end ofsaid cylinder as said platform apparatus moves vertically with respectto said submersible eans.

12. The platform apparatus according to claim 11 wherein said pistonrequires a period of time to move from one end of the cylinder to theother end of the cylinder longer than the time of the longest seas to beencountered by said apparatus.

13. The platfonn apparatus according to claim 12 wherein said period oftime is at least 15 seconds.

14. The platform structure according to claim 9 wherein said submersiblemeans includes a cup-shaped chamber for each of said plurality ofcolumnar support members and each of said support members has a memberrounded at one end for fitting into said chamber, whereby saidtelescoping action is slowed down as said rounded member enters saidchamber.

15. A mobile marine platform apparatus, comprising:

an elevated platform structure adapted to support supplies andequipment;

a plurality of columnar members fixedly secured to said platformstructure, whereby said platform structure is maintained above thesurface of the water;

a mat assembly fixedly secured to said columnar members and parallel tosaid platform structure, said mat assembly being adapted to be loweredto a given depth beneath the surface of water while always floatingabove the water floor, wherein said mat assembly comprises at least onemetal plate having a plurality of freeing holes therein.

16. The apparatus according to claim 15 wherein some of said holes havebeen selectively closed to achieve optimum stability in a given seacondition.

17. A mobile marine platform apparatus, comprising:

an elevated platform structure adapted to support supplies andequipment;

a single vertical columnar member fixedly secured at its upper end tosaid platform structure whereby said elevated platform structure ismaintained above the surface of the water;

a metal plate fixedly secured to the lower end of said columnar memberand parallel to said platform structure, said metal plate having aplurality of freeing holes therein; and

means to cause said mat assembly to be lowered further in the watershort of the ocean floor.

18. The apparatus according to claim 17 wherein some of said holes havebeen selectively closed to achieve optimum stability in a given seacondition.

19. A mobile marine platform apparatus, comprising;

an elevated platform structure adapted to support supplies andequipment;

at least one buoyant structure fixedly secured to the underside of saidplatform structure, being maintained a given distance from said platformstructure;

a plurality of columnar members adapted to move with respect to saidplatform structure;

a mat assembly fixedly secured to said columnar members and parallel tosaid platform structure;

means to lower said mat assembly in the water;

means to secure said platform structure to said columnar members; and

means to release said means to secure said platform structure to saidcolumnar members, whereby said mat may be lowered further in the watershort of the water floor after said at least one buoyant structure hassettled into the water without a further lowering of said platformstructure, wherein said mat assembly comprises at least one metal platehaving a plurality of freeing holes therein.

20. The apparatus according to claim 19 wherein some of said holes havebeen selectively closed to achieve optimum stability in a given seacondition.

1. A mobile marine platform apparatus, comprising: a platform structureadapted to support supplies and equipment; a plurality of telescopingcolumnar members, each being fixedly secured at its upper end to saidplatform structure; a buoyant, ballastable structure fixedly secured tothe lower end of each of said columnar members, including means toballast and deballast said ballastable structure to submerged andfloating positions, respectively; and a second buoyant structure fixedintermediate the ends of at least one of said columnar members tofloatably support said platform apparatus when said ballastablestructure is submerged a predetermined distance.
 2. A mobile marineplatform apparatus, comprising: a platform structure adapted to supportsupplies and equipment; a plurality of telescoping columnar members,each being fixedly secured at its upper end to said platform structure;a buoyant, ballastable structure fixedly secured to the lower end of atleast one of said columnar members, including means to ballast anddeballast said ballastable structure to submerged and floatingpositions, respectively; and a second buoyant structure fixedintermediate the ends of at least one of said columnar members tofloatably support said platform apparatus when said ballastablestructure is submerged a predetermined distance.
 3. A mobile marineplatform apparatus, comprising: a platform structure adapted to supportsupplies and equipment; a plurality of telescoping columnar members,each being fixedly secured at its upper end to said platform structure;a plurality of buoyant, ballastable structures, each of said ballastablestructures being fixedly secured to the lower end of at least one ofsaid columnar members, including means to ballast and deballast saidballastable structures to submerged and floating positions,respectively; and a flotation structure fixed intermediate the ends ofat least one of said columnar members to floatably support said platformapparatus when said ballastable structures are submerged a predetermineddistance.
 4. The apparatus according to claim 3 wherein said pluralityof ballastable structures comprises a pair of parallel pontoons.
 5. Theapparatus according to claim 4, including in addition thereto, aperforated mat connected between said parallel pontoons.
 6. A mobilemarine platform apparatus, comprising: a platform structure adapted tosupport supplies and equipment; a plurality of telescoping columnarmembers; a buoyant, ballastable structure fixedly secured to the lowerend of at least one of said columnar members, including means to ballastand deballast said ballastable structure to submerged and floatingpositions, respectively; and a second buoyant structure fixedintermediate the ends of at least one of said columnar members tofloatably support said platform apparatus when said ballastablestructure is submerged a predetermined distance, said platform structurebeing fixedly attached to said second buoyant structure.
 7. A mobilemarine platform apparatus, comPrising: a platform structure adapted tosupport supplies and equipment; a plurality of columnar members; abuoyant, ballastable structure comprising a plurality of pontoons, andincluding in addition thereto, a perforated mat connected between saidpontoons, fixedly secured to the lower end of at least one of saidcolumnar members, including means to ballast and deballast saidballastable structure between varying depths of submersion; a secondbuoyant structure fixed intermediate the ends of at least one of saidcolumnar members to floatably support said platform apparatus when saidballastable structure is submerged a predetermined distance, saidplatform structure being fixedly attached to said second buoyantstructure.
 8. A mobile marine platform apparatus, comprising: a platformstructure adapted to support supplies and equipment; a plurality ofcolumnar members; a buoyant, ballastable structure comprising a pontoonhaving a center portion comprised of a perforated mat, fixedly securedto the lower end of at least one of said columnar members, includingmeans to ballast and deballast said ballastable structure betweenvarying depths of submersion; a second buoyant structure fixedintermediate the ends of at least one of said columnar members tofloatably support said platform apparatus when said ballastablestructure is submerged a predetermined distance, said platform structurebeing fixedly attached to said second buoyant structure.
 9. A mobilemarine platform apparatus, comprising: a platform structure adapted tosupport supplies and equipment; a plurality of telescoping columnarsupport members, each being fixedly secured at its upper end to saidplatform structure, whereby the profile of the platform remainssubstantially constant regardless of the telescoping positions of saidsupport members; and submersible means fixedly secured to the lower endsof said support members for extending said support members beneath thesea while maintaining said platform structure at or above the surface ofthe sea.
 10. The platform apparatus according to claim 9, including inaddition thereto at least one action snubber member connected betweensaid platform structure and said submersible means.
 11. The platformapparatus according to claim 10 wherein said action snubber comprises aliquid filled piston and cylinder having means for said fluid to movefrom one end of said cylinder to the other end of said cylinder as saidplatform apparatus moves vertically with respect to said submersiblemeans.
 12. The platform apparatus according to claim 11 wherein saidpiston requires a period of time to move from one end of the cylinder tothe other end of the cylinder longer than the time of the longest seasto be encountered by said apparatus.
 13. The platform apparatusaccording to claim 12 wherein said period of time is at least 15seconds.
 14. The platform structure according to claim 9 wherein saidsubmersible means includes a cup-shaped chamber for each of saidplurality of columnar support members and each of said support membershas a member rounded at one end for fitting into said chamber, wherebysaid telescoping action is slowed down as said rounded member enterssaid chamber.
 15. A mobile marine platform apparatus, comprising: anelevated platform structure adapted to support supplies and equipment; aplurality of columnar members fixedly secured to said platformstructure, whereby said platform structure is maintained above thesurface of the water; a mat assembly fixedly secured to said columnarmembers and parallel to said platform structure, said mat assembly beingadapted to be lowered to a given depth beneath the surface of waterwhile always floating above the water floor, wherein said mat assemblycomprises at least one metal plate having a plurality of freeing holestherein.
 16. The apparatus according to claim 15 wherein some of saidholes have been selectively closeD to achieve optimum stability in agiven sea condition.
 17. A mobile marine platform apparatus, comprising:an elevated platform structure adapted to support supplies andequipment; a single vertical columnar member fixedly secured at itsupper end to said platform structure whereby said elevated platformstructure is maintained above the surface of the water; a metal platefixedly secured to the lower end of said columnar member and parallel tosaid platform structure, said metal plate having a plurality of freeingholes therein; and means to cause said mat assembly to be loweredfurther in the water short of the ocean floor.
 18. The apparatusaccording to claim 17 wherein some of said holes have been selectivelyclosed to achieve optimum stability in a given sea condition.
 19. Amobile marine platform apparatus, comprising; an elevated platformstructure adapted to support supplies and equipment; at least onebuoyant structure fixedly secured to the underside of said platformstructure, being maintained a given distance from said platformstructure; a plurality of columnar members adapted to move with respectto said platform structure; a mat assembly fixedly secured to saidcolumnar members and parallel to said platform structure; means to lowersaid mat assembly in the water; means to secure said platform structureto said columnar members; and means to release said means to secure saidplatform structure to said columnar members, whereby said mat may belowered further in the water short of the water floor after said atleast one buoyant structure has settled into the water without a furtherlowering of said platform structure, wherein said mat assembly comprisesat least one metal plate having a plurality of freeing holes therein.20. The apparatus according to claim 19 wherein some of said holes havebeen selectively closed to achieve optimum stability in a given seacondition.